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PubMed1989

Suicide trends in Canada and West Germany: an application of configural frequency analysis.

Canadian and West German successful suicides for the years 1974-1977 were used to fit a log-linear model relating age, method of suicide, gender, and country to suicide frequency. Configural frequency analyses (CFA) were performed to complement the log-linear analyses, as well as to obtain more information about the data. A log-linear model involving all four three-way interactions among these variables was required to explain the observed frequency distribution in a satisfactory manner. Results from this study support McIntosh and Santos's (1982) findings that each gender displays its own unique pattern of methods of suicide. This study also showed that each group has its own unique pattern of methods of suicide within each specific gender group. Results from CFA showed different patterns in the trends of suicide for each age x gender x country x method of suicide grouping. These results can be used to help clarify the intricate relationships among the factors that are important in explaining suicide trends.

Adolescent↗
PubMed2001

Threonine requirements of different broiler genotypes.

The objectives of this work were to study the responses of one Leghorn and two broiler stocks and sexes to different levels of Thr and to estimate their requirements for this amino acid. All experiments were conducted with birds from 1 to 18 d of age. Body weight gain (BWG) and feed consumption were measured on the eighteenth day, and feed conversion ratio (FCR) was calculated. At Day 18, three birds per replicate were killed, and liver and fat pads were collected and weighed. The data were analyzed by the general linear model and nonlinear model procedures of SAS software, and the broken-line linear model was used to estimate Thr requirements of chicks. Experiment 1 had a 5 x 3 factorial design with five levels of Thr (0.63, 0.70, 0.77, 0.84, and 0.91% of the diet), two broiler genotypes (Arbor Acres Classic and High Yield), and one Leghorn genotype (Hy-line W-36), with three replicate pens of eight male birds each. The basal diet was composed of corn, peanut meal (PNM), poultry by-product meal, poultry fat, DL-Met, L-Lys, and L-Ile (23% CP and 3.2 kcal/g of ME). The Leghorn chicks did not respond to Thr supplementation, indicating their requirement was < or = 0.63%. High Yield birds had better BWG and FCR than Classic. The BWG and FCR were reduced more in Classic than High Yield strains by the lowest Thr level. The percentage of liver was higher in the Classic than High Yield strain broilers with Thr supplementation. The second experiment (2 x 2 x 2 factorial design) was conducted to evaluate the effects of two levels of Thr (0.63 and 0.90%), two levels of Ile (0.72 and 0.90%), and two broiler strains (as Experiment 1). There were no responses to Ile for any parameters measured. Experiment 3 (6 x 2 factorial design, corn, PNM-based basal diet) had six Thr levels (0.63, 0.67, 0.71, 0.75, 0.79, and 0.83%) and two broiler strains (as Experiment 1), with four replicate pens of eight male birds each. The High Yield strain broilers grew significantly better at the lowest Thr level, but performance was similar at the higher Thr levels (significant interaction, P = 0.018). FCR was affected by Thr level but not by strain. The Thr requirement of the Classic strain broilers was 0.69 +/- 0.01% for BWG and 0.68 +/- 0.01% for FCR. The Thr requirement of the High Yield strain broilers was 0.68 +/- 0.01% for BWG and 0.69 +/- 0.01% for FCR. The Thr requirements of male versus female High Yield strain broilers were evaluated in a 6 x 2 factorial design, with six Thr levels (Experiment 4), with four replicate pens of eight birds each. Males and females had the same performance and carcass composition results (P > 0.05), except for percentage abdominal fat pads. The Thr requirement was 0.71 +/- 0.01% for BWG and 0.71 +/- 0.01% for FCR for the males and 0.72 +/- 0.008% for BWG and 0.71 +/- 0.001% for FCR for females. Excellent performance was observed from the corn- and PNM-based diet supplemented to contain 0.72% Thr. The Thr requirements of High Yield and Classic broilers (males and females) were similar and greater than for the Leghorn strain studied.

Aging↗
PubMed2003

Demographic characteristics and trends in the prevalence of low birth weight from singleton pregnancies in Taiwan, 1978-1997.

BACKGROUND AND PURPOSE: Low birth weight (LBW) has adverse influences on lifetime health. This study examined trends in LBW in Taiwan between 1978 and 1997, and assessed the risk of LBW associated with gender, birth order of infant, and parental age at delivery. METHODS: Information on live born singletons for the study period was retrieved from the Taiwan birth registry. We calculated biannual trends for overall LBW rates and for specific demographic factors. Log-linear models with a Poisson assumption were used to assess the linear trend of the LBW rates and the interaction between time and selected demographic factors. Log-linear models were also used to estimate the independent effect of individual demographic factors on the risk of LBW. RESULTS: The LBW prevalence declined from 6.78% (55,694/820,364) in 1978-79 to 4.95% (30,907/623,971) in 1996-97, representing a 27.10% reduction. The prevalence of LBW showed a noticeable reduction between the late 1970s and mid-1980s, and appeared homogeneous after the mid-1980s. This declining trend was evident for almost all of the selected demographic factors. The only exception was in infants born to teenage fathers, which showed a 10.59% increase in prevalence of LBW during the 20-year study period. Infants born to mothers or fathers aged 35 and above had the greatest reduction (47.58% and 41.44%, respectively) in the rate of LBW, whereas teenage mothers had the lowest reduction (11.75%) in the rate of LBW. CONCLUSIONS: Parental age at an infant birth has a strong association with reduction of LBW risk. Education programs focusing on the problem of teenage pregnancy may accelerate the reduction of LBW.

Adolescent↗
PubMed1997

Small sample inference for fixed effects from restricted maximum likelihood.

Restricted maximum likelihood (REML) is now well established as a method for estimating the parameters of the general Gaussian linear model with a structured covariance matrix, in particular for mixed linear models. Conventionally, estimates of precision and inference for fixed effects are based on their asymptotic distribution, which is known to be inadequate for some small-sample problems. In this paper, we present a scaled Wald statistic, together with an F approximation to its sampling distribution, that is shown to perform well in a range of small sample settings. The statistic uses an adjusted estimator of the covariance matrix that has reduced small sample bias. This approach has the advantage that it reproduces both the statistics and F distributions in those settings where the latter is exact, namely for Hotelling T2 type statistics and for analysis of variance F-ratios. The performance of the modified statistics is assessed through simulation studies of four different REML analyses and the methods are illustrated using three examples.

Analysis of Variance↗
PubMed1995

Alcohol consumption and all-cause mortality.

BACKGROUND: Prospective studies of alcohol and mortality in middle-aged men almost universally find a U-shaped relationship between alcohol consumption and risk of mortality. This review demonstrates the extent to which different studies lead to different risk estimates, analyses the putative influence of abstention as a risk factor and uses available data to produce point and interval estimates of the consumption level apparently associated with minimum risk from two studies in the UK. METHOD: Data from a number of studies are analysed by means of logistic-linear modelling, taking account of the possible influence of abstention as a special risk factor. Separate analysis of British data is performed. RESULTS: Logistic-linear modelling demonstrates large and highly significant differences between the studies considered in the relationship between alcohol consumption and all-cause mortality. The results support the identification of abstention as a special risk factor for mortality, but do not indicate that this alone explains the apparent U-shaped relationship. Separate analysis of two British studies indicates minimum risk of mortality in this population at a consumption level of about 26 (8.5 g) units of alcohol per week. CONCLUSIONS: The analysis supports the view that abstention may be a specific risk factor for all-cause mortality, but is not an adequate explanation of the apparent protective effect of alcohol consumption against all-cause mortality. Future analyses might better be performed on a case-by-case basis, using a change-point model to estimate the parameters of the relationship. The current misinterpretation of the sensible drinking level of 21 units per week for men in the UK as a limit is not justified, and the data suggest that alcohol consumption is a net preventive factor against premature death in this population.

Adult↗
PubMedDate not supplied

Optimized partition of minimum spanning tree for piecewise modeling by particle swarm algorithm. QSAR studies of antagonism of angiotensin II antagonists.

In quantitative structure-activity relationship (QSAR) modeling, when compounds in a training set exhibit a significant structural distinction between each other, in particular when chemicals of biological interest interacting on the receptor involve a different mechanism, it might be difficult to construct a single linear model for the whole population of compounds of interest with desired residuals. Developing a piecewise linear local model can be effective to circumvent the aforementioned problem. In this paper, piecewise modeling by the particle swarm optimization (PMPSO) approach is applied to QSAR study. The minimum spanning tree is used for clustering all compounds in the training set to form a tree, and the modified discrete PSO is applied to divide the tree to find satisfactory piecewise linear models. A new objective function is formulated for searching the appropriate piecewise linear models. The proposed PMPSO algorithm was used to predict the antagonism of angiotensin II. The results demonstrated that PMPSO is useful for improvement of the performance of regression models.

Algorithms↗
PubMed2004

Model for oxygen transfer in rotating biological contactor.

Rotating biological contactor is being widely used for wastewater treatment but there is an apparent lack of knowledge about the rate at which oxygen transfer occurs, in physical and biological system. In this study the transfer of oxygen from air to water by a rotating disc air-liquid contactor in physical system is investigated. The oxygen transfer model suggested by Kim and Molof, Water Sci. Technol. 14 (1982) 569, was modified and the developed model is termed as modified Kim and Molof model. The model was calibrated by using available data in literature and validated by experiments conducted in this study. The effect of significant physical parameters was integrated into a single term and is termed as volume renewal number. The modified Kim and Molof model was compared with the other available models. The coefficient of determination (R(2)) for the modified Kim and Molof model obtained is 0.95 which is much higher than in the other available models. Thereby the model is expected to estimate oxygen transfer more accurately. Further, a simplified linear model between K(L)a and the volume renewal number is proposed. Both modified Kim and Molof and linear model estimate the overall oxygen transfer coefficient (K(L)a) accurately.

Biomass↗
PubMed1986

The use of nonmetric variation in estimating human population admixture: a test case with Brazilian blacks, whites, and mulattos.

Measurements in populations which serve as valid indicators of biological relationship should be proportional to genetic distance. In order to test the utility of discrete cranial traits for estimating genetic distances among populations, estimates of admixture are obtained for gene frequency data and nonmetric cranial data in São Paulo mulattos (M). The gene frequency data serve as a control that the three populations are related as stated: estimates of admixture are obtained by using São Paulo whites (W) and blacks (B) as parental populations and by estimating the parameter of admixture, m, in the model pM = (1 - m) pW + mpB (Elston, 1971) where the p's are either gene frequencies or nonmetric trait frequencies. A test of goodness of fit of the model provides a means of ascertaining whether or not the data fit this linear model. While the gene frequency data indicate distances among the three populations which are highly compatible with the linear model of admixture, the nonmetric data show significant deviations from the model. This implies that the frequencies of the nonmetric traits in the populations used in this analysis are not a linear function of genetic distance. This discourages the use of nonmetric traits in making quantitative conclusions about genetic relationships. It also suggests the need for investigation of the use of other skeletal characters for estimating genetic distance, as well as approaches for such investigations through the study of hybrid individuals.

Adult↗
PubMed1994

A general theory for modeling capture-recapture data from a closed population.

A general theory for estimating the size of a closed population from multiple-recapture data is presented. This theory is easily extended to open population models for multiple-recapture data. Estimation is based on a log-linear model developed for modeling dependent capture-recapture data when capture probabilities vary temporally with behavioral response and are heterogeneous among animals. Models for complete capture history data are developed along with the first log-linear models for removal data. The maximum likelihood estimator of the model parameters along with the estimated covariance matrix are presented.

Animal Identification Systems↗
PubMed1989

A review of methods for misclassified categorical data in epidemiology.

Misclassification introduces errors in categorical variables. This paper presents a review of methods for misclassified categorical data in epidemiology. Different sampling schemes for a 2 x 2 x 2 table and methods of analyses will be discussed first. A misclassification matrix is defined, and the usual misclassification models will be shown to be a subclass of log-linear models. Well-known results on a 2 x 2 table with misclassification and recent results on a 2 x 2 x 2 table are then reviewed. Finally two methods of adjusting for misclassification will be given. The first method assumes a known misclassification matrix, and the second method uses subsampling to estimate the misclassification matrix. The analysis is based on a recursive system of log-linear models: first determine a misclassification model, then select a model for the correctly classified variables. The methods are illustrated by data from traffic safety research on the effectiveness of seatbelt use in reducing injuries.

Biometry↗
PubMed1999

Dynamics of primate P retinal ganglion cells: responses to chromatic and achromatic stimuli.

1. The majority of primate retinal ganglion cells (RGCs) project to the parvocellular layers of the lateral geniculate nucleus (LGN). These P cells play a central role in early visual processing. 2. An improved method of systems analysis has allowed us to explore the dynamics of the colour-opponent subregions of P-cell receptive fields with a single chromatic stimulus. The data show that the centre and surround subregions of the P-cell receptive field have similar temporal responses, but the surround is slightly delayed. The centre and surround demonstrate a large degree of chromatic selectivity. 3. The responses of the centre and surround subregions were fitted with a linear model and the model was used to predict the responses of P cells to new chromatic and achromatic stimuli. Although linear models predict the chromatic responses well, simple linear combinations of centre and surround responses fail to predict P-cell responses to achromatic stimuli. 4. The temporal responses of the different subpopulations of P cells, such as ON/OFF or L-centre/M-centre were not significantly different.

Animals↗
PubMed2004

Formulation of medium constituents by multiresponse analysis of central composite design to enhance chitinase production in Pantoea dispersa.

In the present study, a high chitinase producing strain Pantoea dispersa was isolated from the sea dumps at Bhavnagar, India. Chitin, urea, CaCl2 and MgSO4 x 7H2O were variables used in central composite design for chitinase production. Chitinase, biomass and pH were the responses used in different models to evaluate individually fit ones. Quadratic model was found to be fit for chitinase response whereas in the case of biomass and pH, linear model was found to be fit without the effect of others. Chitinase production was optimized with respect to other responses such as biomass and pH in multiresponse analysis of response surface design by using desirability approach. In multiresponse analysis, following medium formulation (g/l), chitin, 15; urea, 0.32; CaCl2, 0.10 and MgSO4 x 7H2O, 0.08 was found to predict optimum chitinase production of 482.77 units/ml with overall highest desirability of 0.854 as compared to other formulations. The selection of model was done on the basis of high Adjusted R-squared value and lowered p-value for each model in individual analysis of each response. In multiresponse experiment, it was found that for response chitinase quadratic model and for responses pH and biomass linear models were well fit. Through desirability analysis, it was found that in the chitinase production, pH was essential as compared to biomass in P. dispersa. Endochitinase and chitobiase actvities were also studied.

Biotechnology↗
PubMed1993

Protein secondary structure from Fourier transform infrared and/or circular dichroism spectra.

A multivariate linear model (Gauss-Markoff model) with noise is used to analyze the estimation of protein secondary structure from spectra of 21 reference proteins whose structures are known from X-ray studies. Fourier transform infrared (FTIR) spectra from 1700 to 1500 cm-1 and circular dichroism (CD) spectra from 178 to 260 nm have been used. The secondary structure categories of interest are alpha-helix, antiparallel beta-sheets, parallel beta-sheets, beta-turns, and "other". The secondary structures are predicted from separate spectra as well as from combined FTIR and CD spectra. The characteristic spectra belonging to the secondary structures and the prediction errors are also estimated. Attention has been paid to the criteria for the choice of rank of matrices of reference spectra, which corresponds to the number of independent pieces of spectral information. Criteria used are: magnitudes of singular values, root mean square error of model fit, relative error of estimable parameters and errors in predicted secondary structure. The ranks of the spectral matrices are found to be between three and six. The model accuracy is determined by removing each protein from the sample and comparing predicted and X-ray values of secondary structure. It is concluded that the linear model is more adequate for the protein FTIR spectra than for the CD spectra. Secondary structure predictions using the FTIR amide I band (1700-1600 cm-1) and the FTIR amide II band (1600-1500 cm-1), or a combination of the two, are of comparable accuracy. In particular, antiparallel beta-sheets and "other" are more reliably estimated from FTIR spectra. However, alpha-helix is more reliably estimated from CD spectra. Combining the spectra yields the best results of both techniques for each class.

Circular Dichroism↗
PubMed1990

The incidence of injuries in young people: II. Log-linear multivariable models for risk factors in a collaborative study in Brazil, Chile, Cuba and Venezuela.

Injuries and accidents are acknowledged as leading causes of morbidity and mortality among children and adolescents in the developing countries of the world. The Pan American Health Organization sponsored a collaborative study in four selected countries in Latin America to study the extent of the problem as well as to examine the potential risk factors associated with selected non-fatal injuries in the countries. The study subjects were injured children and adolescents (0-19 years of age) presenting at the study hospitals in chosen urban centres, as well as injured that were surveyed in households in the catchment areas of the hospitals. Study methods and descriptive frequency results were presented earlier. In this paper, log-linear multivariate regression models are used to examine the potentiating effects within country of several measured variables on specific types of injuries. The significance of risk factors varied between countries; however, some general patterns emerged. Falls were more likely in younger children, and occurred at home. The main risk factor for home accidents was the age of the child. The education of the head of the household was an important risk factor for the type of injury suffered. The likelihood of traffic accident injury varied with time of day and day of the week, but also was more likely in higher educated households. The results found are consistent with those found in other studies in the developed world and suggest specific areas of concern for health planners to address.

Accidents↗
PubMed1999

Evaluation of the angiotensin challenge methodology for assessing the pharmacodynamic profile of antihypertensive drugs acting on the renin-angiotensin system.

AIMS: The performance of the experimental paradigm of angiotensin challenges with continuous non-invasive blood pressure measurement was evaluated. Angiotensin dose-response relationships were characterized, along with the influence of clinical covariates. The stability of angiotensin-induced peaks and the variability of the angiotensin doses were assessed. Finally, the predictive value of studies based on angiotensin challenges to determine drug doses effective in therapeutics was evaluated. METHODS: The data were gathered from 13 clinical studies on nine angiotensin II receptor antagonists, one ACE inhibitor and one dual ACE-NEP inhibitor, using Finapres for measuring the response to exogenous angiotensin challenges. Modelling of angiotensin dose-response curves and determination of the inter and intrasubject variability were performed by nonlinear regression (NONMEM). The different sources of variations in angiotensin I and II doses and angiotensin-induced peaks were evaluated by analyses of variance. The dose of ACE inhibitors and angiotensin II receptor antagonists inhibiting blood pressure increase by at least 75%, as measured by this method, was chosen for comparison with the labelled starting dose. RESULTS: Angiotensin challenges exhibited a clear dose-response relationship which can be characterized both by an Emax or a log linear model. The log linear model gave an average systolic/diastolic response of 24+/-6/20+/-5 mmHg for a unit dose of 1 microgram of angiotensin II equivalents, and an increase of 6/6 mmHg for each doubling of the dose. The angiotensin ED50 calculated values were 0.67 microgram for systolic and 0.84 microgram for diastolic blood pressure. The angiotensin doses for eliciting a given response and the angiotensin induced peaks were fairly constant between period and subject, but vary significantly between studies. Based on an inhibition of blood pressure by 75%, the agreement was good between the doses of ACE inhibitors and angiotensin receptor antagonists predicted from studies using the methodology of angiotensin challenges and the doses shown to be clinically efficacious, in spite of high intersubject and intrasubject variabilities. CONCLUSIONS: This experimental method represents a valid surrogate for the therapeutic target and a useful tool for the pharmacokinetic and pharmacodynamic profiling of drugs acting on the renin-angiotensin system.

Angiotensin II↗
PubMed1996

Evidence for a non-linear relationship between leg strength and gait speed.

Although the relationship between strength and physical performance in older adults is probably non-linear, few empirical studies have demonstrated that this is so. In a population-based sample of adults aged 60-96 years (n = 409), leg strength was measured in four muscle groups (knee extensor, knee flexor, ankle plantar flexor, ankle dorsiflexor) of both legs using an isokinetic dynamometer. A leg strength score was calculated as the sum of the four strength measurements in the right leg. Usual gait speed was measured over a 15.2 metre course. With a linear model, leg strength explained 17% of the variance in gait speed. Non-linear models (quadratic and inverse) explained significantly more variance (22%). The nature of the non-linear relationship was that, in stronger subjects, there was no association between strength and gait speed, while in weaker subjects, there was an association. Body weight and age also explained significant amounts of variance in gait speed, while sex and height did not. The results supported the hypothesis of a non-linear relationship between leg strength and gait speed that is similar for older men and women. This finding represents a mechanism for how small changes in physiological capacity may have substantial effects on performance in frail adults, while large changes in capacity have little or no effect in healthy adults.

Adult↗